. >>> plans to analyze the genetic make-up of newtown gunman lanza, are causing a stir. looking at his dna could reveal a mutation that is responsible for aggressive or violent behavior. others say this is no proof a marker exists and people with similar markers could be segregated. >>> san francisco's railway offered free rides. muni's west growth shaped city neighborhoods. >> reporter: it was surprisingly uncrowded all day. we found tourists, especially gleeful at the free rides. >> i have ridden it one time today. it was free. we went the wrong direction but i guess it does not matter today. >> reporter: the 1years is often little appreciated story of reshaping san francisco. nothing more important than the twin peaks tunnel. from market street to the westportal neighborhood. we dug into the archives. a century ago southwest san francisco was virtually all sand dunes. and development required public transit. the longest rail tunnel west of new york city. 2 and a quarter miles. three years to build. this film of real estate promotion from the time, opening in 1918, the